Manufacture of fuse powder and fuses



l atenteci eia. l4,

MANUFACTURE-F FUSE rown'iiit AND FUSES Henryk Zenftman, Saltcoats,Scotland, assig'nor to Imperial Chemical Industries Limited, a cor 7poration of Great Britain No Drawing. Application October 6, 1944,Serial No. 557,560. In Great Britain October 6, 1943 10 Claims. (01. 52-2) considerable variation in their burning properties according to theprevailing atmospheric pressure,

which frequently causes inconvenience in -blast-" ing at high altitudesand in the production of military fuses. Mixtures of oxidising andreducing agents that react together with the formation of little or nogaseous products are free from this objection, and it has been proposedto em ploy as fuse compositions mixtures consisting of red lead andsilicon. The reaction may be represented by the equation Unfortunatelythe range of fuse speeds that can be obtained in mixtures of red leadand silicon by variation in the relative proportions of two ingredientsis very limited, and the burning speed at atmospheric pressure of fusesmade from even the slowest burning mixtures composed of 'red lead andsilicon is substantially faster than that of ordinary black powder fuse.

It is known that mixtures of silicon and potassium nitrate are capableof reacting exothermically when they are strongly heated, but theycannot be used as fuse compositions sincethey are incapable ofpropagating the reactionprogressively through a train of small crosssectional area. This reaction proceeds with the evolution" of gas andthe formation of a glowing residue, and may be represented as follows: a

I have now found that by using potassium nitrate and red lead togetheras oxidising agents for silicon fuse compositions, fuses capable ofburning vigorously at a wide rangeof burning speeds are obtained, andmore particularly-the production of fuses burning vigorouslyatlowerspeeds than those that can be obtained by the use of mixtures ofred lead and silicon alone, is

facilitated.

According to the present inventlon fus-co rnpositions comprise apulverulent mixture of potas sium nitrate, red lead and silicon, g

The amounts of potassium nitrate, red leada d silicon can lie between50-15%, 30-60% and 10-40%, respectively, and preferably between -55 tionin the atmospheric pressure.

40-20%, 40-60% and 20-30%, respectively.

The burning speeds of the resulting fus powders depend both on therelative amounts of potassium nitrate and red lead present in theoxidising component of the mixture, and on the silicon content of thecomposition. The minimum fuse speeds that can be attained becomeprogressively slower as the potassium nitrate content of the oxidisingcomponent is increased towards the limit that can be tolerated withoutrendering the composition incapable of propagating the reaction alongthe fuse. Up to a point the effect of excess of silicon over thestoichiometric proportion, calculated from the foregoing equations, isto increase the fuse speeds; but as the excess of silicon isprogressively increased the resulting fuse speeds approach a maximum,and may become slower before sufficient silicon has been included in thecomposition to render the fuse incapable of burning steadily.

For any particular proportion of potassium nitrate in the oxidisingcomponent it is preferable to employ a composition containing the lessof any two excesses of silicon that will give a fuse of the desiredspeed, since the resulting fuse composition will be the more vigorouslyburning of the two.

But the presence of progressively increasing proportions of potassiumnitrate renders it possible to include progressively higher amounts ofexcess silicon in the mixture.

When the ratio of'the amount of potassium nitrate to that of red. leadis low, no excess of silicon over the stoichiometric proportion need beemployed, or it may even be permissible that there should be a slightdeficiency of silicon, but as the potassium nitrate content of theoxidising component is increased it becomes necessary to employ aprogressively increasing excess of silicon to render the fuse powdercapable of propagating the reaction. The maximurn excess of silicon thatcan be used without rendering the fuse incapable of propagating thereaction also increases.

The fuse compositions produced according to the present invention yielda certain amount of gas amongst the products of their combustion, thusproviding for end spit, a characteristic absolutely indispensable innon-detonating fuse in order that it may be operative to set off adetonator into which it may be crimped. But, by means of the invention,it is possible to obtain fuse compositions burning at speeds comparablewith those obtained from black powder fuse compositions, that aresubstantially less liable to variation in their burning properties withvaria- This is bei cause, in the new fuse compositions, the gaseouscomponent of the products of combustion can be so much smaller inproportion to the total amount of said products than is the case withblack powder fuse.

In putting the invention into effect the pulverulent ingredients may bemixed together in any order but preferably the pulverulent mixture isproduced by first admixing potassium nitrate and red lead and thereafteradmixing this mix-r ture with silicon. The fuses may be made with a coreof the pulverulent fuse composition in powder or rod form containing .abinding agent, or preferably with corned granules containing gum,nitrocellulose or an artificial resin, in the customary fashion; but thecomposition may also be made into an imporgus mass bymeans of athermoplastic binding agent, for instance a gelatinised nitrocellulosecomposition, -.so that it can be extruded at arsuitably raisedtemperature to forma core around which anenvelope is applied. It will beunderstood that the burning speed of the fuse so produced may differconsiderably-from that of fusehaving a core of the powder or corned:fuse composition.

For the purposeof studyand-comparison of the burning speedsof thesecompositions, a testing method known as the lead fuse test may be used.

In this test, lead tubes of specified size and weight are filled withthefuse powder to'be tested, and are sealedand drawn through dies untilthey have-been reduced to aspecified standard diameter. -middle portionofthe filled and drawn tube, and

Measured=lengthstare then cut from the the speed of burning of theselengths is then measured at any-desired pressure.

Since the lead sheath is melted bythe heat of combustion of the fusepowder, thegaseous combustion-products aresubstantially unconfined andthe burning takes placeunder-the prevailing barometrio pressure.

The burningspeedsof the fuse made in accordance with the presentinvention maybe somewhat increasedby embeddinginthe .core a soft=metalwire, for instance of 20 19040 standard wire gauge diameter.

' The invention is illustrated :by the following -examples,- in whichthe parts are parts: by weight:

Exampl 1 .Thefu e powder i m de b m siee ed l ficatiqn s eve. ndsili onsv sl t pass a itis Standard ecifica on Sieve In t jesidis ns. com onen tredl ad and t e po s- .sium nitrate r resent in h pro o tion 78.52 1 ndhen ili a in var u ron on f om i met c u wa s- .Th lea fuse .speeds ofthe resulti g fuse powders at one atmosphere pressure are approximatelyas follows:

The; ingredients usednare the-same as,in Example ..;1, but th redeadandnot ssiu nitrate i e 1*. we sees 31 are used in the proportions71.422815. The lead fuse speeds of the resulting fuse powders at oneatmosphere pressure are approximately as follows:

Percentage S Silicon r-gconds Excess Per Yard :In we ab e cen an 9i silo h l fuse-failstopropa ate.

E mp eh ingre ie ts u ed are thesa e a n EX- nle bu th red ea and P tasi n t are used in-theproportions of 55.534 5. The lead fus -s eeds .qfh resnltiqs f se wqde s t n atm sphere P eset? .ep mxima el a 1.-

-:9 spqn2 n ls diyse speeds e iuse 991E1- ro iti ps-rnadswith es 1 1 andsi con on .:ra-. ee'.-fm.a 32 st second .ner a d with .1 excess silicoto ab. t 131; seconds per yard with 35 .ate Thec n ssiti s .QtEx mrfle 1containi om tow-pe entexcssss at s ,qqmpe iiiqns Ex m leq nta s supl 60e cent. assess sil lcnnrand' these o conta nin u to oi exc lle tqual-.ity .whenihet zm wi .ORS e nss lwith sum a provided t wate w n ted textl envelqps after thefashion custom rily employed for the manufacture ofsafety-fuse from black powder.

ss ssg silken that see he ;cllid. d is .ws than-tin the eas 9f lea fushus wh n ll lfl p red ead onota smm u e huminsstees et a ou can be ob ane b use of a eitdffseciid's per :3.% excess. of silicon,

item??? 4.

100 C. The red lead and the potassium nitrate are present in theproportions 55.5:44.5. The ratio of the amounts of powder to bindingagent is 70:20, and the approximate diameter of the extruded fuse coreis 0.06 inch. In the pulverulent ingredients the silicon is present inan excess of 12.5 per cent over the theoretical. The extruded corecomposition is coated with a textile covering spun around it and theenvelope is waterproofed. The resulting fuse has a speed of about 320seconds per yard at one atmosphere pressure.

Example 5 The procedure is the same as in Example 4, but the diameter ofthe extruded core is .08 inch. The relative proportions of red lead andpotassium nitrate and the ratio of powder to binding agent are the sameas in Example 4, but the excess of silicon is 8 per cent. The burningspeed of the resulting fuse is about 475 seconds per yard at oneatmosphere pressure.

Example 6 The procedure is the same as in Example 4. The diameter of thecore is .08 inch and the proportions of red lead to potassium nitrateand of powder to binding agent are the same as in Example 4, but theexcess of silicon is 4 per cent. The burning speed of the resulting fuseis about 660 seconds per yard.

Example 7 The procedure is the same as in Example 4, except that thecore is extruded around a. 30 standard wire gauge copper wire passingcentrally through the die. The diameter of the core is .05 inch, the redlead and the potassium nitrate are present in the ratio 71.4:28.6 andthe silicon is present in an excess of 23 per cent. The ratio of powderto binding agent is 75:20. The resulting fuse has a speed ofapproximately 33 seconds per yard at atmospheric pressure and 38 secondsper yard at one third of an atmosphere pressure.

I claim:

1. Fuse compositions comprising a pulverulent mixture of potassiumnitrate, red lead and silicon, wherein the proportions by weight of theingredients in the order named lie between 50-15%, 30-60 and 10-40respectively.

2. Fuse compositions as claimed in claim 1 wherein the amounts ofpotassium nitrate, red

6 lead and silicon lie between 40-20%, 40-50% and 20-30%, respectively.

3. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is in the form of corned granules containing a binding agent.

4. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is bound together in rod form by means of a binding agent.

5. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is in homogeneous admixture with a suflicient quantity of athermoplastic binding agent to form an imporous plastic mass capable ofextrusion.

6. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is in the form of corned granules containing a binding agent,and the proportions of potassium nitrate, red lead and silicon liebetween 40-20%, 40-50% and 20-30%, respectively.

7. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is bound together in rod form by means of a binding agent, andthe proportions of potassium nitrate, red lead and silicon lie between40-20%, 40-50% and 20-30%, respectively.

8. Fuse compositions as claimed in claim 1 wherein the said pulverulentmixture is in homogeneous admixture with a sufiicient quantity of athermoplastic binding agent to form an imporous plastic mass capable ofextrusion, and the proportions of potassium nitrate, red lead andsilicon lie between 40-20%, 40-50% and 20-30%, respectively.

9. Non-detonating fuse containing the fuse composition set forth inclaim 1.

10. Non-detonating fuse containing the fuse composition set forth inclaim 1, wherein the proportions of potassium nitrate, red lead andsilicon lie between 40- 0%, 40-50% and 20-30%,

respectively.

HENRYK ZENIF'IMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. FUSE COMPOSITIONS COMPRISING A PULVERULENT MIXTURE OF POTASSIUMNITRATE, RED LEAD AND SILICON, WHEREIN THE PROPORTIONS BY WEIGHT OF THEINGREDIENTS IN THE ORDER NAMED LIE BETWEEN 50-15% 30-60% AND 10-40%,RESPECTIVELY.